1. Field of the Invention
This invention relates to technologies for measuring temperature of a gas, and especially for measuring extremely low temperatures.
2. Background of the Invention
There are a wide range of instruments and devices employed to measure temperature for scientific and engineering purposes. Common techniques employed for measuring temperatures of large amounts or samples of liquid or gas include use of expansive metals and thermocouples.
In techniques employing expansive metals, a metal which has a measurable coefficient of expansion relative to temperature, such as mercury, is immersed in the sample of gas or liquid to be measured. After allowing the metal time to reach the mean temperature of the sample material, the length or size of the piece of metal is measured, usually optically, and correlated to an known expansion chart or graph to determine the temperature of the sample material.
Thermocouples provide an electronic method for measuring temperature, in which a bimetallic junction is employed to measure temperature of a gas or liquid sample. Two dissimilar metals are joined together, such as by vacuum deposit or by melting, to form a junction which generates a tiny electromotive force (“EMF”) according to the temperature of the junction. In some situations, two wires of differing metals are twisted together, thereby forming the mechanical junction between the metals, and secured in place through applying a small amount of epoxy to the twisted area. The junction is immersed in the sample liquid or gas, allowed time to assume the temperature of the sample material, and a millivoltmeter is used to measure the EMF of the junction. This is correlated to a known characteristic profile of the junction EMF to temperature to arrive at a temperature measurement.
Both the thermocouple and the expansive metal approaches, however, have the possibility of changing the temperature of the sample being measured, especially for very small samples of gas or liquid. This disadvantage arises out of the fact that the thermocouple or metal each contains its own amount of thermal energy prior to being immersed in the sample material, and when immersed, adds (or subtracts) thermal energy to (or from) the sample material in order to assume the same temperature of the sample.
Additionally, these methods require a waiting period for the measuring device to equalize with the temperature of the sample, which may not be conducive to processes requiring more rapid temperature measurements for purposes of process control, manufacturing automation, etc.
For extremely low temperatures, these devices and techniques are inadequate. For example, many research experiments, fabrication processes, and reactions are undertaken at temperatures well below 0 Celsius, approaching just a few hundred degrees Kelvin. In such a situation, measuring the temperature of the gas or solid under test or within the reaction poses special problems, as most methods of probing the gas or solid create the potential of changing the temperature, or require structures too small for practical implementation.
One known technique for such low temperature applications and small sample size measurement has been proposed by Thurber, et al., in “Temperature Measurement at the End of a Cantilever Using Oxygen Paramagnetism in Solid Air” of the U.S. Army Research Laboratory. It employs a small amount of frozen air doped onto or around a small sample. The sample is placed at the end of a thin cantilever structure. Oxygen is known to be weakly diamagnetic in a manner related to temperature at extremely low temperatures (e.g. where oxygen is a solid). Thus, the cantilever containing the frozen-oxygen doped sample is measurably deflected an amount due to the paramagnetic attraction of the oxygen to another magnetic source. The deflection amount of the cantilever is correlated to a known function of oxygen paramagnetic properties with respect to temperature to arrive at a temperature of the sample.
This approach, while useful for cantilever magnetometry and Magnetic Resonance Force Microscopy (“MRFM”) experiments, suffers from a number of limitations and disadvantages. Most notably, it is not operable at sample temperatures above the temperature of sublimation of oxygen, and thus is not useful for a wide range of interesting applications. Additionally, it is not applicable to scenarios where a thin cantilever device is impractical.
Therefore, there is a need in the art for a system and method of quickly measuring temperature, including very low temperatures as well as higher temperatures, of a small volume of gas or liquid, without removing or adding a substantial amount of heat to the sample material from the measuring device.